The present invention relates to a method and apparatus for producing an optical disk base to store, record, and retrieve sounds, images, and information.
An optical disk base used to make a digital audio disk, video disk, optical disk recording medium, and opto-magnetic disk is a transparent plate, about 1 mm thick, with grooves or pits (information pattern) formed on the surface thereof.
An optical disk base is produced by one of the following known methods. (1) By injecting a polymeric material such as polycarbonate and polymethyl methacrylate into a mold provided therein with a metal stamper having an information pattern in the form of grooves or pits. [See Nikkei Mechanical, p. 34 (1982.2.1) and Nikkei Electronics, p. 133 (1982.6.7).](2) By attaching a photo-curable resin thin film having an information pattern to the surface of a previously prepared transparent base. (See Japanese Patent Laid-open No. 86756/1978 and Japanese Patent Laid-open No. 152028/1980.) (3) By injecting a photo-curable resin into a cavity formed between a stamper having an information pattern and a transparent flat plate, and subsequently curing the photo-curable resin with light energy supplied through the transparent flat plate, and finally removing the stamper and transparent flat plate to give a transparent plate of photo-cured resin having an information pattern.
However, the first method has a disadvantage that the resulting optical disk base tends to be optically anisotropic because it is difficult to completely remove the molecular orientation that takes place while the polymeric material flows and solidifies. Another disadvantage is that the information pattern is not accurately transferred from the stamper to the base, and this leads to an optical disk of poor performance.
The second method also has a disadvantage that transparent bases have to be prepared beforehand, which adds to the number of steps and makes the process complex and costly.
By contrast, the third method has the possibility of eliminating these disadvantages. According to the third method as illustrated in FIGS. 6(a) and 6(b), a photocurable resin is injected from a gate 4 into the mold cavity formed by a transparent plate (such as glass plate) 1 and a stamper 2 having an information pattern, said transparent plate and stamper being placed opposite to each other with a peripheral ring 3 interposed between them. After injection, the resin is cured with light energy supplied from a light source 6.